Cytokines are a superfamily of small proteins synthesized and secreted by different cells, which participate in the proliferation and differentiation of many kinds of cells and play essential roles in physiological and pathological processes. Cytokines include interleukins, colony stimulating factors, interferons, tumor necrosis factors, growth factors and chemokines. Many kinds of recombinant cytokines and their antagonists produced by using genetic engineering technology have been applied to clinical treatment and have enjoyed positive effects. This reflects the spacious applications of cytokines.
The superfamily of chemokine (also called chemotactic factor) comprises dozens of polypeptides with molecular weights of 8-12 KD. These polypeptides are similar in structure and in their chemotactic effects, and they play important roles in immune defense, immunoregulation, inflammation, hematopoietic regulation and vasculogenesis. The amino acid sequences of most of the chemokines share the same character of conserved four-cysteine (Cys) motif. According to the positions of the first and the second Cys, chemokines can be divided into four subfamilies named CXC, CC, CX3C and C, respectively, wherein C represents Cys and X represents any kind of amino acid. The members of CXC, such as IL-8, interferon-induced protein 10 (IFN-IP-10), and cytokine with melanocyte growth stimulating activity (MGSA) have their encoding genes usually located on chromosome 4 in human somatic cells, and activate and attract neutrophils and T lymphocytes. While the numbers of CC, such as macrophage inflammatory protein-1α (MIP-1α), macrophage inflammatory protein-1β(MIP-1 β), monocyte chemoattractant protein-1(MCP-1) and cytokine regulated on activation, and normal T cell expressed and secreted (RANTES) have their encoding genes usually located on chromosome 17 in somatic cells, and mainly activate monocytes, lymphocytes, basophils and eosinophils. Fractalkine is the only identified member of the CX3C subfamily, which can activate and chemotacte T cells and monocytes. As for the C subfamily, only Lymphotactin (Ltn) is presently found, which can chemotacte lymphocytes.
The receptors of chemokines belong to the superfamily of GTP-binding protein which have the characteristic of seven transmembrane domains. In accordance with the specific combination to different numbers of chemokine subfamilies, chemokine receptors are named: CXC Receptor (CXCR), such as CXCR 1, CXCR 2, CXCR 3, and CXCR 4; CC Receptor (CCR), such as CCR 1, CCR 2, CCR 3, CCR 4, CCR 5, CCR 6 and CCR 7; CX3C Receptor (CX3CR) (See Marco, B., et al., 1997, Human Chemokines: An Update Annu. Rev. Immunol. 15:675-705). Because chemokines play important roles in system immunization, inflammatory responses and hematopoietic regulation, some abnormal changes of chemokines or their receptors (e.g., the defect of chemokines or chemokine receptors, or the overexpression of chemokines, or the increase of soluble chemokine receptors) always result in some kind of infectious disease or autoimmune disease, or sometimes even in tumors. Therefore, the detection of chemokines or chemokine receptors can be used in clinical diagnosis to observe the development of diseases and to judge the curative effects. Recent studies show that HIV can invade the immune cells of human by combining with chemokine receptors, which indicate that chemokine receptors as well as chemokines are closely related to the infection and development of HIV disease. Hence, Chemokines could be used as promising drugs to block the invasion of HIV to immune cells (Cocchi, F., et al., 1995, “Identification of RANTES, MIP-1α, and MIP-1β as the Major HIV-Suppressive Factors Produced by CD8+T Cells,” Science 270:1811). Furthermore, some chemokine drugs produced by bioengineering methods have been successively used in clinical tests and have the possibility to become useful medicines in the future. For instance, myeloid progenitor inhibitory factor-1 (MPIF-1) has been used as a protective hematopoietic drug in high-dose radiotherapy or chemotherapy for tumors (Marshall, A., 1998, “HGS launches “first” genomics product in clinic,” Nat. Biotechol. 16:129).
The present invention is based on the finding that many types of cytokines or chemokines can be stimulated by phytohemagglutinin (PHA) (Brantschen, S., et al., 1989, “Differential expression of cytokine mRNAs cell lines,” Lymphokine Res 8(3):163-72), while interleukin-10(IL-10) is a broad-spectrum inhibitor of cytokines (Di-Hwei, H., et al., 1990, Science 250:830). By using suppression subtractive hybridization (SSH) technique, some novel cytokines could be found. (Diatchenko, L., et al, 1996, “Suppression subtractive hybridization: A method for generating differentially regulated or tissue-specific cDNA probes and libraries,” Pro. Natl Acad. Sci. USA 93:6025-30). Based on the above, the present inventors, by using SSH technique, identified and cloned CKLF1 gene from a cDNA library derived from U937 cell line, a human promonocytic cell line. Furthermore, the inventors disclose the biological activity and function of CKLF1 and its variants.